1. Field of the Invention
The present invention relates to a method for producing a silicon single crystal in which the silicon single crystal is pulled in accordance with the Czochralski method (hereinafter referred to as the CZ method), and which can reduce the density and size of crystal defects, called grown-in defects, generated in the crystal in the course of the pulling operation, thereby enabling production of a silicon single crystal having an excellent oxide dielectric breakdown voltage characteristics. The present invention also relates to a silicon single crystal and silicon wafers produced by the method.
2. Description of the Related Art
In order to cope with an increase in the degree of fineness and the degree of integration of semiconductor circuits, quality requirements are recently becoming severer on silicon single crystals which are used as a base material. Particularly, there has been required a reduction in density and size of grown-in defects such as flow pattern defects (FPD), laser scattering tomography defects (LSTD), and crystal originated particles (COP). In order to meet such a requirement, various measures have been employed.
For example, in order to decrease the above-described defects, there may be used a technique disclosed in Japanese Patent Application Laid-Open (kokai) No. 8-337490, in which the time for passing through a temperature zone of 1150-1080.degree. C. during pulling of a single crystal is increased. This technique was developed as a result of investigations and studies regarding the relationship between the thermal history of a silicon single crystal during the growth thereof and introduced crystal defects. For example, when the time for passing through the 1150-1080.degree. C. temperature zone was made equal to or greater than 60 minutes, the FPD density decreased from 1000 defects/cm.sup.2 to 400 defects/cm.sup.2. The good chip yield in terms of oxide-film dielectric breakdown strength--which can be used as a parameter for evaluating device characteristics--increased from a level below 50% to a level greater than 80%.
Meanwhile, recent studies have revealed that although the density of defects is decreased as the time for passing through the 1150-1080.degree. C. temperature zone is increased, the size of the defects increases. That is, changing the length of the time for passing through the temperature zone causes only a change in the ratio between the density and size of crystal defects but does not cause a change in the total volume of the crystal defects.
The oxide dielectric breakdown voltage characteristics--which can be used as a parameter for evaluating device characteristics--has a strong correlation with the density of crystal defects, and a better oxide dielectric breakdown voltage characteristics is obtained when the defects are relatively large in size and low in density. Therefore, in order to improve the oxide dielectric breakdown voltage characteristics, there has been employed a measure in which the density of defects is decreased at the sacrifice of an increase in the size of the defects.
However, it recently has been reported that defects having a larger size, called COP (Crystal Originated Particles), cause adverse effects on semiconductor devices. Therefore, there has arisen a requirement for concurrently achieving reduction of the density of defects or improvement of the dielectric breakdown strength, and reduction of the size of the defects.